1. Field of the Invention
The present invention relates to highly toughened alumina sintered bodies and to a manufacturing method therefor, and more particularly to a novel method for manufacturing alumina sintered bodies in which abrasion powder and other byproducts worn from grinding media always brought about as contamination during the pulverization or grinding of starting powders are efficiently utilized, which allows the same low-temperature sintering as that achieved with highpurity, readily sinterable aluminum oxide powders to be applied to .alpha.-aluminum oxide powders fabricated using inexpensive aluminum hydroxide produced by the Bayer's process as a starting material, and which makes it possible to obtain alumina sintered bodies with high strength and fracture toughness; and relates to highly toughened alumina sintered bodies thus obtained.
The highly toughened alumina sintered bodies of the present invention can be used as a structural material or substrate material with high mechanical strength and reliability requirements.
2. Description of the Background
The following are examples of reports describing conventional alumina sintered bodies.
These examples include techniques in which several percent of silicon oxide, magnesium oxide, or other glass-forming compounds are added to an .alpha.-aluminum oxide powder fabricated by heating and pyrolyzing an aluminum hydroxide produced by the Bayer's process as a starting material, and sintered bodies are fabricated using a liquid phase formed at a high temperature; and techniques in which the aforementioned powder is pulverized into a fine powder, and solid-phase sintering is then performed without any additions or with an addition of a small amount of magnesium oxide (T. Furubayashi, K. Yamada, "New Technologies for Advanced Materials: Development, Manufacture, Assessment"; Edited by G. Adachi, K. Shibayama, and T. Minami, Kagaku Dojin Publishing House, Tokyo, 1981, pp. 35-59).
It has also been reported that highly toughened alumina sintered bodies can be obtained by low-temperature sintering through the use of a high-purity .alpha.-aluminum oxide powder fabricated without the use of the Bayer's process (S. Kato, T. Iga, "Effect of Crystallinity of NH.sub.4 AlO(OH)HCO.sub.3 Matrix Salt on Sinterability of .alpha.-Alumina," Yogyo Kyokaishi, 85 (6) 253-257, 1977).
Such conventional alumina sintered bodies, however, have a fracture toughness of about 3.5 MPa.multidot.m.sup.1/2. For example, a sintered body fabricated from a conventional high-purity, readily sinterable aluminum oxide powder is a material that has high strength but low fracture toughness (see, for example, R. Morrell, "Handbook of Properties of Technical & Engineering Ceramics. Part 2. Data Reviews. Section 1. High-alumina Ceramics," Her Majesty's Stationery Office. London, 1987; Edited by H. Okuda, T Hirai, and T. Kamijo, "Structural Ceramic Materials," Ohm Publishing Company, Tokyo, 1987; and M. Yasuoka, Manuel E. Brito, K. Hirao, and S. Kanzaki, "Effect of Dispersed Particle Diameter on Mechanical Properties of Alumina Containing Dispersed Non-oxide Particles," J. Ceram. Soc. Jpn., 101 (8), 889-894, 1993).
In addition, highly strengthened, highly toughened zirconia is expensive, has inferior mechanical characteristics due to the effect of low-temperature heating or atmosphere, and cannot be used in a wide variety of applications (see, for example, P. F. Bevher, "Microstructural Design of Toughened Ceramics," J. Am. Ceram. Soc., 74 (2), 255-69, 1991).
An urgent need therefore existed for developing inexpensive structural materials having high strength and high fracture toughness, and for developing alumina sintered bodies in particular.
In view of this situation, the inventors, in the course of a study on alumina sintered bodies, turned their attention to the efficient use of abrasion powder worn from grinding media for starting powders, and research extensively the effects on the properties of such alumina sintered bodies. As a result, the inventors perfected the present invention upon discovering that a structural material with high fracture toughness can be obtained by adding and sintering a prescribed proportion of abrasion powder worn from alumina balls or another product as seed crystals for .alpha.-aluminum oxide.